1. Field of the Invention
The present invention relates in general to a throttle valve control system of an automotive internal combustion engine, and more particularly to a control system which, under a given condition of the associated motor vehicle, reduces automatically the opening degree of the throttle valve irrespective of operation of an accelerator pedal.
2. Description of the Prior Art
Hitherto, in motor vehicles powered by an internal combustion engine, a traction control system has been proposed and put into a practical use which controls the driving torque of the engine in accordance with the driving force actually needed by the vehicle under running. Such control systems are very useful in controlling the vehicle which is under running on a slippery road, such as, a iced road and a snow-covered road.
One of such control systems are of a type which has, in addition to a first throttle valve directly controlled by an accelerator pedal, a second throttle valve connected in series with the first throttle valve. That is, when, under running of the vehicle, a slip of road wheels of the vehicle is detected, the control system reduces the opening degree of the second throttle valve to reduce the driving torque of the engine thereby lowering the driving force of the vehicle. With this, undesired swerving phenomenon of the vehicle is suppressed or at least minimized. However, due to provision of the second throttle valve, the entire of the control system become large in size.
In order to solve such drawback in size, Japanese Patent First Provisional Publication 3-61654 proposes another control system which uses only one throttle valve. That is, under normal cruising condition of the vehicle, the opening degree of the throttle valve is directly controlled by the accelerator pedal. While, upon sensing the need of the traction control, the opening degree of the throttle valve is automatically controlled or reduced irrespective of operation of the accelerator pedal. In the control system proposed by the publication, a butterfly-type throttle valve is employed which is connected to a spring-biased throttle shaft to pivot therewith. By the spring, the throttle valve is biased in a direction to close the associated throat. An operation lever actuated by the accelerator pedal is pivotally connected to the throttle shaft, and a control lever actuated by an electronically controlled actuator is connected to the throttle shaft. A so-called "lost motion lever" is further connected to the throttle shaft, which becomes engaged with the operation lever in response to pivoting of the operation lever in the valve closing direction. A lost motion spring is interposed between the operation lever and the lost motion lever to bias them in a direction to establish engagement therebetween.
However, in the control system of the above-mentioned Japanese publication, the throttle valve arrangement needs a number of parts and thus the construction of the arrangement becomes very complicated. Furthermore, due to increase in number of the parts used, the arrangement needs greater assembly time and thus greater cost.
In view of the above-mentioned drawbacks possessed by the conventional systems, the inventors have proposed a new control system which is shown in Japanese Patent First Provisional Publication 5-248275. In this new system, the number of parts used is reduced.